Optical detection of interrupted fluid flow to ablation probe

ABSTRACT

An electrosurgical system includes an electrosurgical device adapted to direct energy to tissue and a fluid path leading to the electrosurgical device. The system also includes an optical sensor unit operably associated with the fluid path. The optical sensor unit includes a light-emitting element to generate light output and a light-receiving element to collect light outputted from the light-emitting element. The light-emitting element and the light-receiving element are disposed such that light output from the light-emitting element passes through the fluid path to the light-receiving element. The optical sensor unit is capable of detecting an air bubble in the fluid path passing through the optical sensor unit using a sensed characteristic of light collected at the light-receiving element.

BACKGROUND

1. Technical Field

The present disclosure relates to detection devices for use inelectrosurgical devices and, more particularly, to systems and methodsfor optical detection of interrupted fluid flow to an ablation probe.

2. Discussion of Related Art

Treatment of certain diseases requires the destruction of malignanttissue growths, e.g., tumors. Electromagnetic radiation can be used toheat and destroy tumor cells. Treatment may involve inserting ablationprobes into tissues where cancerous tumors have been identified. Oncethe probes are positioned, electromagnetic energy is passed through theprobes into surrounding tissue.

In the treatment of diseases such as cancer, certain types of tumorcells have been found to denature at elevated temperatures that areslightly lower than temperatures normally injurious to healthy cells.Known treatment methods, such as hyperthermia therapy, heat diseasedcells to temperatures above 41° C. while maintaining adjacent healthycells below the temperature at which irreversible cell destructionoccurs. These methods involve applying electromagnetic radiation toheat, ablate and/or coagulate tissue. Microwave energy is sometimesutilized to perform these methods. Other procedures utilizingelectromagnetic radiation to heat tissue also include coagulation,cutting and/or ablation of tissue.

Electrosurgical devices utilizing electromagnetic radiation have beendeveloped for a variety of uses and applications. A number of devicesare available that can be used to provide high bursts of energy forshort periods of time to achieve cutting and coagulative effects onvarious tissues. There are a number of different types of apparatus thatcan be used to perform ablation procedures. Typically, microwaveapparatus for use in ablation procedures include a microwave generatorthat functions as an energy source, and a microwave surgical instrument(e.g., microwave ablation probe) having an antenna assembly fordirecting the energy to the target tissue. The microwave generator andsurgical instrument are typically operatively coupled by a cableassembly having a plurality of conductors for transmitting microwaveenergy from the generator to the instrument, and for communicatingcontrol, feedback and identification signals between the instrument andthe generator.

There are several types of microwave probes in use, e.g., monopole,dipole and helical, which may be used in tissue ablation applications.In monopole and dipole antenna assemblies, microwave energy generallyradiates perpendicularly away from the axis of the conductor. Monopoleantenna assemblies typically include a single, elongated conductor. Atypical dipole antenna assembly includes two elongated conductors, whichare linearly aligned and positioned end-to-end relative to one anotherwith an electrical insulator placed therebetween. Helical antennaassemblies include a helically-shaped conductor that can be formed invarious configurations. The main modes of operation of a helical antennaassembly are normal mode (broadside), in which the field radiated by thehelix is maximum in a perpendicular plane to the helix axis, and axialmode (end fire), in which maximum radiation is along the helix axis.

A microwave transmission line typically includes a thin inner conductorthat extends along the longitudinal axis of the transmission line and issurrounded by a dielectric material and is further surrounded by anouter conductor around the dielectric material such that the outerconductor also extends along the transmission line axis. In onevariation of an antenna, a waveguiding structure, such as a length oftransmission line or coaxial cable, is provided with a plurality ofopenings through which energy “leaks” or radiates away from the guidingstructure. This type of construction is typically referred to as a“leaky coaxial” or “leaky wave” antenna.

Cooling the ablation probe may enhance the overall heating pattern ofthe antenna, prevent damage to the antenna and prevent harm to theclinician or patient. Because of the small temperature differencebetween the temperature required for denaturing malignant cells and thetemperature normally injurious to healthy cells, a known heating patternand precise temperature control is needed to lead to more predictabletemperature distribution to eradicate the tumor cells while minimizingthe damage to surrounding normal tissue.

Fluid cooled or dielectrically buffered microwave devices may be used inablation procedures. During operation of a microwave ablation device, ifproper cooling is not maintained, e.g., flow of coolant or bufferingfluid is interrupted, the microwave ablation device may exhibit rapidfailures due to the heat generated from the increased reflected power. Acoolant fluid having entrained gas bubbles may be circulated from acooling system into a microwave ablation device. When a bubble filledwith even a small volume of air or multiple air bubbles in closeproximity to each other are introduced into an ablation probe, e.g.,when the ablation probe is operating at a high power level, the ablationprobe may be susceptible to rapid failure due to overheating conditions.The time to failure is dependant on the power delivered to the antennaand degree to which coolant flow is reduced and/or the duration of theinterruption.

SUMMARY

The present disclosure relates to an electrosurgical system including anelectrosurgical device adapted to direct energy to tissue and a fluidpath leading to the electrosurgical device. The system also includes anoptical sensor unit operably associated with the fluid path. The opticalsensor unit includes a light-emitting element to generate light outputand a light-receiving element to collect light outputted from thelight-emitting element. The light-emitting element and thelight-receiving element are disposed such that light output from thelight-emitting element passes through the fluid path to thelight-receiving element. The optical sensor unit is capable of detectingan air bubble in the fluid path passing through the optical sensor unitusing a sensed characteristic of light collected at the light-receivingelement.

The present disclosure also relates to a method of detecting an airbubble in a fluid flow including the step of providing an optical sensorunit including a light-emitting element and a light-receiving element,the optical sensor unit operably associated with a fluid path. Themethod also includes the steps of determining a first reference valuebased on air flow in the fluid path passing through the optical sensor,determining a second reference value based on fluid flow in the fluidpath passing through the optical sensor unit, using the optical sensorunit to monitor the fluid flow in the fluid path to detect an air bubblein the fluid flow using at least one of the first reference value or thesecond reference value, and when an air bubble in the fluid flow isdetected by the optical sensor unit, outputting an electrical signalfrom the optical sensor unit.

The present disclosure also relates to a method of detecting an airbubble in a fluid flow including the step of providing a fluid sourcefor supplying a fluid and providing an optical sensor unit including alight-emitting element and a light-receiving element, the optical sensorunit operably associated with a first fluid path, the first fluid pathleading from the fluid source to an electrosurgical device. The methodalso includes the steps of: performing a first calibration step bydirecting light from the light-emitting element through air flow in thefirst fluid path passing through the optical sensor unit and sensing acharacteristic of light collected at the light-receiving element todetermine a first reference value; performing a second calibration stepby directing light from the light-emitting element through fluid flow inthe first fluid path passing through the optical sensor unit and sensinga characteristic of light collected at the light-receiving element todetermine a second reference value; operating the optical sensor unit todirect light from the light-emitting element through the first fluidpath passing through the optical sensor unit and to sense acharacteristic of light collected at the light-receiving element todetermine a third reference value; and controlling an electrosurgicalgenerator based on a comparison result of a comparison of the thirdreference value to the first and second reference values.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects and features of the presently disclosed systems and methods foroptical detection of interrupted fluid flow to an electrosurgical devicewill become apparent to those of ordinary skill in the art whendescriptions of various embodiments thereof are read with reference tothe accompanying drawings, of which:

FIG. 1 is a schematic diagram of an electrosurgical system including acoolant supply system according to an embodiment of the presentdisclosure;

FIG. 2 is an enlarged view of the indicated area of detail of FIG. 1according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of an electrosurgical system including acoolant supply system according to another embodiment of the presentdisclosure;

FIG. 4 is a flowchart illustrating a method of detecting an air bubblein a fluid flow according to an embodiment of the present disclosure;

FIG. 5 is a flowchart illustrating an embodiment of the step ofdetermining a first reference value and a second reference value of themethod illustrated in FIG. 4 according to the present disclosure; and

FIG. 6 is a flowchart illustrating a method of detecting an air bubblein a fluid flow according to another embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Hereinafter, embodiments of the presently disclosed systems and methodsfor optical detection of interrupted fluid flow to an electrosurgicaldevice are described with reference to the accompanying drawings. Likereference numerals may refer to similar or identical elements throughoutthe description of the figures. As shown in the drawings and as used inthis description, and as is traditional when referring to relativepositioning on an object, the term “proximal” refers to that portion ofthe apparatus that is closer to the user and the term “distal” refers tothat portion of the apparatus that is further from the user.

Electromagnetic energy is generally classified by increasing energy ordecreasing wavelength into radio waves, microwaves, infrared, visiblelight, ultraviolet, X-rays and gamma-rays. As it is used in thisdescription, “microwave” generally refers to electromagnetic waves inthe frequency range of 300 megahertz (MHz) (3×10⁸ cycles/second) to 300gigahertz (GHz) (3×10¹¹ cycles/second). As it is used in thisdescription, “ablation procedure” generally refers to any ablationprocedure, such as microwave ablation, radio frequency (RF) ablation ormicrowave ablation-assisted resection.

Light may be regarded as an electromagnetic wave that travels instraight lines (gravity and electromagnetic influences excepted) untilit is either reflected or refracted. Refraction of light occurs when alight wave travels from a medium with a given refractive index to amedium with another refractive index. As it is used in this description,“refraction” generally refers to the change in direction of a wave dueto a change in its speed, as occurs when a wave passes from one mediumto another. As it is used in this description, “refractive index”generally refers to a measure of how much the speed of light is reducedinside a medium, compared to the speed of light in vacuum or air.

As it is used in this description, “light source” generally refers toall illumination sources including photo-luminescent sources,fluorescent sources, phosphorescence sources, lasers,electro-luminescent sources, such as electro-luminescent lamps, andlight-emitting diodes. As it is used in this description,“light-emitting diode” generally refers to any system that is capable ofreceiving an electrical signal and producing a color of light inresponse to the signal. Thus, “light-emitting diode”, as used herein,includes light-emitting diodes (LEDs) of all types, including whiteLEDs, infrared LEDs, ultraviolet LEDs, visible color LEDs,light-emitting polymers, semiconductor dies that produce light inresponse to current, organic LEDs, electro-luminescent strips, siliconbased structures that emit light, and other such systems. As it is usedin this description, “color” generally refers to any frequency ofelectromagnetic radiation, or combination of different frequencies,within the visible light spectrum, the infrared and ultraviolet areas ofthe spectrum, and in other areas of the electromagnetic spectrum whereillumination sources may generate radiation.

As it is used in this description, “optical detector” generally refersto a device that converts an optical signal into an electrical signal.As it is used in this description, “transmission line” generally refersto any transmission medium that can be used for the propagation ofsignals from one point to another. As it is used in this description,“fluid” generally refers to a liquid, a gas or both.

Various embodiments of the present disclosure provide electrosurgicaldevices for treating tissue and systems and methods for opticaldetection of interrupted fluid flow to the electrosurgical devices, suchas ablation probes. Embodiments may be implemented using electromagneticradiation at microwave frequencies or at other frequencies. Anelectrosurgical system including an energy applicator in fluidcommunication with a coolant supply system, according to variousembodiments, is designed and configured to operate between about 500 MHzand about 10 GHz. The coolant supply system, as described herein, may beused in conjunction with various types of devices, such as microwaveantennas having either a straight or looped radiating antenna portion,etc.

Various embodiments of the presently disclosed electrosurgical systemsincluding an energy applicator in fluid communication with a coolantsupply system are suitable for microwave ablation and for use topre-coagulate tissue for microwave ablation assisted surgical resection.Although various methods described hereinbelow are targeted towardmicrowave ablation and the complete destruction of target tissue, it isto be understood that methods for directing electromagnetic radiationmay be used with other therapies in which the target tissue is partiallydestroyed or damaged, such as, for example, to prevent the conduction ofelectrical impulses within heart tissue. In addition, although thefollowing description describes the use of a dipole microwave antenna,the teachings of the present disclosure may also apply to a monopole,helical, or other suitable type of microwave antenna.

FIG. 1 shows an electrosurgical system 10 according to an embodiment ofthe present disclosure that includes an energy applicator or probe 100.An embodiment of an energy applicator, such as the probe 100 of FIG. 1,in accordance with the present disclosure, is shown in more detail inFIG. 2. It will be understood, however, that other probe embodiments mayalso be used.

Probe 100, which is described in more detail later in this disclosure,generally includes an antenna assembly 12 having a radiating portionconnected by a feedline 110 (or shaft) via a transmission line 15 to aconnector 16, which may further operably connect the probe 100 to apower generating source 28, e.g., a microwave or radio frequency (RF)electrosurgical generator. Feedline 110 may be coupled to a coolant port51 to facilitate the flow of coolant or buffering fluid into, and outof, the probe 100.

Electrosurgical system 10 in accordance with an embodiment of thepresent disclosure includes a power generating source 28, a coolantsupply system 11 adapted to provide coolant fluid “F” to the probe 100,and a sensor unit 46 capable of detecting a gas bubble in the coolantsupply system 11. In some embodiments, the sensor unit 46 iselectrically coupled to the power generating source 28, and may beconfigured to generate an alarm signal to the power generating source 28and, in response thereto, control logic, which may be associated withthe power generating source 28, may reduce the power output, e.g., for apredetermined time interval or until a manual reset switch is actuated.

In some embodiments, the coolant supply system 11 includes a coolantsource 18, and may include a substantially closed loop having a firstcoolant path 19 leading to the probe 100 and a second coolant path 20leading from the probe 100. The size and shape of the first coolant path19 and the second coolant path 20 may be varied from the configurationdepicted in FIG. 1. Sensor unit 46 may be configured to detect an airbubble in close proximity to the coolant source 18.

Coolant port 51 may be in fluid communication with the coolant source 18via the first coolant path 19 and/or the second coolant path 20. In someembodiments, the coolant supply system 11 includes a first coolant path19 and a second coolant path 20, wherein the first coolant path 19includes a coolant supply line 31 leading from the coolant source 18 toa coolant inlet port 52 that is defined in the coolant port 51, and thesecond coolant path 20 includes a coolant return line 35 leading from acoolant outlet port 53 that is defined in the coolant port 51 to thecoolant source 18.

Coolant source 18 may be any suitable housing containing a reservoir ofcoolant fluid “F”. Coolant fluid “F” may be any suitable fluid that canbe used for cooling or buffering the probe 100, e.g., deionized water,or other suitable cooling medium. Coolant fluid “F” may have dielectricproperties and may provide dielectric impedance buffering for theantenna assembly 12. Coolant fluid “F” may be a conductive fluid, suchas a saline solution, which may be delivered to the target tissue, e.g.,to decrease impedance and allow increased power to be delivered to thetarget tissue. A coolant fluid “F” composition may vary depending upondesired cooling rates and the desired tissue impedance matchingproperties. Various fluids may be used, e.g., liquids including, but notlimited to, water, saline, perfluorocarbon, such as the commerciallyavailable Fluorinert® perfluorocarbon liquid offered by Minnesota Miningand Manufacturing Company (3M), liquid chlorodifluoromethane, etc, inother variations, gases (such as nitrous oxide, nitrogen, carbondioxide, etc.) may also be utilized as the cooling fluid. In yet anothervariation, a combination of liquids and/or gases, including, forexample, those mentioned above, may be utilized as the coolant fluid“F”.

As shown in FIG. 1, a fluid movement device 34 may be provided in thefirst coolant path 19 to move the coolant fluid “F” through the firstcoolant path 19. Fluid movement device 34 may include valves, pumps,power units, actuators, fittings, manifolds, etc. The position of thefluid movement device 34 may be varied from the configuration depictedin FIG. 1. Fluid movement device 34 may additionally, or alternatively,be provided in the second coolant path 20. Although the coolant supplysystem 11 shown in FIG. 1 includes a single, fluid movement device 34positioned in the first coolant path 19, various combinations ofdifferent numbers of fluid movement devices, variedly sized and variedlyspaced apart from each other, may be provided in the first coolant path19 and/or the second coolant path 20.

Sensor unit 46 may be disposed at any suitable position to allow for thedetection of a gas bubble in the coolant supply system 11. In someembodiments, the sensor unit 46 is disposed such that a gas bubble inthe coolant supply system 11 can be detected before the bubble can beintroduced into the probe 100. Sensor unit 46 may be disposed in thefirst coolant path 19, and may be disposed in close proximity to thecoolant source 18. In some embodiments, the sensor unit 46 iselectrically coupled to the power generating source 28, and thedetection of a bubble may trigger an alarm signal to the powergenerating source 28. Electrical characteristics of the power generatingsource 28 may be controlled in response to the alarm signal. In someembodiments, the electrosurgical system 10 reduces the power and/orvoltage output of the power generating source 28, thereby reducingenergy applicator power output to a low level, in response to the alarmsignal. In some embodiments, the sensor unit 46 includes an opticaldetector, and may be used to monitor the coolant fluid “F” flow in thecoolant supply line 31 to detect the presence of air or other gas withinthe coolant fluid “F” flow.

Audible indicatory means may be incorporated or associated with theelectrosurgical system 10 to notify the operator of the bubblecondition. In such case, the operator may take steps, e.g., performvisual inspection of the coolant fluid “F” in the coolant source 18and/or visual inspection of the first coolant path 19, or portionsthereof, to verify that the coolant supply system 11 is functioningproperly. A “reset” button (not shown) may be provided to allow thepower generating source 28 to return to normal mode.

In the illustrated embodiment, sensor unit 46 generally includes a lightsource or light-emitting element 43 (also referred to herein as opticaltransmitter 43) and a light receiving element 40 (also referred toherein as optical receiver 40). Optical transmitter 43 may include anysuitable device configured to transmit optical signals, e.g., alight-emitting diode (LED) 42. Optical receiver 40 may include anysuitable device configured to receive optical signals, e.g., aphoto-diode 41. In some embodiments, an LED 42 and a photo-diode 41 arearranged on opposite sides of a coolant line, e.g., the coolant supplyline 31. LED 42 may be configured to transmit either a continuous orpulsed optical signal through the coolant supply line 31. Photo-diode 41may be positioned to receive the transmitted optical signal on theopposite side of the coolant supply line 31 from the LED 42. A fixturehousing an LED 42 and photo-diode 41 pair may be provided to allow thesensor unit 46 (also referred to herein as optical detector 46) to beclipped or otherwise fastened to a portion of the coolant supply line31, e.g., to provide reliable orientation and shield the opticaldetector 46 from ambient light interference.

In accordance with embodiments of the present disclosure, an air orother gas bubble may be detected by the optical detector 46 by eithersignal intensity or signal position at the optical receiver 40. Air andliquids have different degrees of attenuation per unit length anddifferent refractive index values (e.g., water has a higher refractiveindex than air). Air has a refractive index of about 1.0003, and waterhas a refractive index of about 1.33. When an air bubble passes throughthe coolant supply line 31, the optical detector 46, according toembodiments of the present disclosure, detects the change in intensityof light collected at the photo-diode 41, compared to the intensity oflight collected at the photo-diode 41 when fluid “F” passes through thecoolant supply line 31. In sensor unit 46 embodiments using signalintensity to detect an air bubble, the change in intensity of lightcollected at the photo-diode 41 is interpreted as indicator of thepresence of an air bubble.

In some embodiments, an LED 42 and a photo-diode 41 are configured tocommunicate when fluid “F” is present in the coolant supply line 31.When an air bubble passes through the coolant supply line 31, the variedrefraction angle deflects light away from its intended photo-diode 41and very little light impinges upon the photo-diode 41. In sensor unit46 embodiments using signal position to detect an air bubble, theabsence of light impinging upon the photo-diode 41 is interpreted asindicator of the presence of an air bubble.

A logic circuit (not shown) in the sensor unit 46 may relay informationthrough digital or analog communication to the power generating source28 indicating whether the optical detector 46 is in the no-bubble stateor bubble state. The optical detector 46 may be a separate device thatplugs into digital or analog inputs on the power generating source 28,programmed according to the communication protocol of the opticaldetector 46.

In some embodiments, the power generating source 28 is configured toprovide microwave energy at an operational frequency from about 500 MHzto about 2500 MHz. In other embodiments, the power generating source 28is configured to provide microwave energy at an operational frequencyfrom about 500 MHz to about 10 GHz. Power generating source 28 may beconfigured to provide various frequencies of electromagnetic energy.Transmission line 15 may additionally, or alternatively, provide aconduit (not shown) configured to provide coolant fluid “F” from thecoolant source 18 to the probe 100.

Feedline 110 may electrically connect the antenna assembly 12 via thetransmission line 15 to the power generating source 28, and may includea coaxial cable, which may be semi-rigid or flexible. Feedline 110 mayhave a variable length from a proximal end of the antenna assembly 12 toa distal end of transmission line 15 ranging from a length of about oneinch to about twelve inches. Feedline 110 may be constructed of avariety of electrically conductive materials, e.g., copper, gold, orother conductive metals with similar conductivity values. Feedline 110may be made of stainless steel, which generally offers the strengthrequired to puncture tissue and/or skin. Conductive materials used toform the feedline 110 may be plated with other materials, e.g., otherconductive materials, to improve their properties, e.g., to improveconductivity or decrease energy loss, etc.

In some embodiments, the feedline 110 includes stainless steel, and toimprove its conductivity, the stainless steel may be coated with a layerof a conductive material such as copper or gold. Feedline 110 mayinclude an inner conductor, a dielectric material coaxially surroundingthe inner conductor, and an outer conductor coaxially surrounding thedielectric material. Antenna assembly 12 may be formed from a portion ofthe inner conductor that extends distal of the feedline 110 into theantenna assembly 12. In one embodiment, the feedline 110 may be formedfrom a coaxial, semi-rigid or flexible cable having a wire with a 0.047″outer diameter rated for 50 Ohms. Feedline 110 may be cooled by fluide.g., saline or water, to improve power handling, and may include astainless steel catheter.

Located at the distal end of the antenna assembly 12 is an end cap ortapered portion 120, which may terminate in a sharp tip 123 to allow forinsertion into tissue with minimal resistance. One example of a straightprobe with a sharp tip that may be suitable for use as the energyapplicator 100 is commercially available under the trademark EVIDENT™offered by Covidien. The end cap or tapered portion 120 may includeother shapes, such as, for example, a tip 123 that is rounded, flat,square, hexagonal, or cylindroconical.

In some variations, the antenna assembly 12 includes a distal radiatingportion 105 and a proximal radiating portion 140. In some embodiments, ajunction 130 couples the proximal radiating portion 140 and the distalradiating portion 105. In some embodiments, the distal and proximalradiating portions 105, 140 align at the junction 130, which isgenerally made of a dielectric material, e.g., adhesives, and are alsosupported by the inner conductor that extends at least partially throughthe distal radiating portion 105. Junction 130, or portions thereof, maybe disposed between the proximal and distal radiating portions, 140 and105. Junction 130 may be formed from any suitable elastomeric or ceramicdielectric material by any suitable process. In some embodiments, thejunction 130 is formed by overmolding and includes a thermoplasticelastomer, such as, for example, polyether block amide (e.g., PEBAX®,manufactured by The Arkema Group of Colombes, France), polyetherimide(e.g., ULTEM® and/or EXTEM®, manufactured by SABIC Innovative Plasticsof Saudi Arabia) and/or polyimide-based polymer (e.g., VESPEL®,manufactured by E. I. du Pont de Nemours and Company of Wilmington,Del., United States). Junction 130 may be formed using any suitableovermolding compound by any suitable process, and may include use of aceramic substrate.

In some embodiments, the antenna assembly 12 may be provided with acoolant chamber (e.g., 337 shown in FIG. 3). Additionally, the junction130 may include coolant inflow and outflow ports (not shown) tofacilitate the flow of coolant into, and out of, the coolant chamber.Examples of coolant chamber and coolant inflow and outflow portembodiments are disclosed in commonly assigned U.S. patent applicationSer. No. 12/401,268 filed on Mar. 10, 2009, entitled “COOLEDDIELECTRICALLY BUFFERED MICROWAVE DIPOLE ANTENNA”, and U.S. Pat. No.7,311,703 entitled “DEVICES AND METHODS FOR COOLING MICROWAVE ANTENNAS”.

In some embodiments, the antenna assembly 12 may be provided with anouter jacket (e.g., 339 shown in FIG. 3) disposed about the distalradiating portion 105, the junction 130 and/or the proximal radiatingportion 140. The outer jacket may be formed of any suitable material,such as, for example, polymeric or ceramic materials. The outer jacketmay be applied by any suitable method, such as, for example, heatshrinking, overmolding, coating, spraying dipping, powder coating,baking and/or film deposition. The outer jacket may be a water cooledcatheter formed of a material having low electrical conductivity.

During microwave ablation, e.g., using the electrosurgical system 10,the probe 100 is inserted into or placed adjacent to tissue andmicrowave energy is supplied thereto. Ultrasound or computed tomography(CT) guidance may be used to accurately guide the probe 100 into thearea of tissue to be treated. Probe 100 may be placed percutaneously oratop tissue, e.g., using conventional surgical techniques by surgicalstaff. A clinician may pre-determine the length of time that microwaveenergy is to be applied. Application duration may depend on many factorssuch as tumor size and location and whether the tumor was a secondary orprimary cancer. The duration of microwave energy application using theprobe 100 may depend on the progress of the heat distribution within thetissue area that is to be destroyed and/or the surrounding tissue.Single or multiple probes 100 may provide ablations in short proceduretimes, e.g., a few minutes, to destroy cancerous cells in the targettissue region.

A plurality of probes 100 may be placed in variously arrangedconfigurations to substantially simultaneously ablate a target tissueregion, making faster procedures possible. Multiple probes 100 can beused to synergistically create a large ablation or to ablate separatesites simultaneously. Tissue ablation size and geometry is influenced bya variety of factors, such as the energy applicator design, number ofenergy applicators used simultaneously, time and wattage.

In operation, microwave energy having a wavelength, lambda (λ), istransmitted through the antenna assembly 12, e.g., along the proximaland distal radiating portions 140, 105, and radiated into thesurrounding medium, e.g., tissue. The length of the antenna forefficient radiation may be dependent on the effective wavelength,λ_(eff), which is dependent upon the dielectric properties of the mediumbeing radiated into. Antenna assembly 12 through which microwave energyis transmitted at a wavelength, λ, may have differing effectivewavelengths, λ_(eff), depending upon the surrounding medium, e.g., livertissue as opposed to breast tissue.

FIG. 3 shows an electrosurgical system 1000 according to an embodimentof the present disclosure that includes an antenna assembly 312substantially disposed within a sheath 338. Antenna assembly 312 issimilar to the antenna assembly 12 shown in FIG. 2 and furtherdescription thereof is omitted in the interests of brevity. In someembodiments, a feedline 110 couples the antenna assembly 312 to aconnection hub 322. Connection hub 322, which is described in moredetail later in this disclosure, generally includes a cable connector379 and fluid ports 330 and 332.

Sheath 338 generally includes a tubular member 339 defining a lumen intowhich the antenna assembly 312, or portion thereof, may be positioned.In some embodiments, the sheath 338 is disposed over and encloses thefeedline 110, the proximal radiating portion 140 and the distalradiating portion 105, and may at least partially enclose the tip 123.In accordance with the embodiment shown in FIG. 3, a coolant chamber 337is defined between the tubular member 339 and the outer surfaces of thefeedline 110, the proximal radiating portion 140 and the distalradiating portion 105. Coolant chamber 337 is adapted to circulatecoolant fluid “F” therethrough, and may include baffles, multiplelumens, flow restricting devices, or other structures that may redirect,concentrate, or disperse flow depending on their shape. Examples ofcoolant chamber embodiments are disclosed in commonly assigned U.S.patent application Ser. No. 12/350,292 filed on Jan. 8, 2009, entitled“CHOKED DIELECTRIC LOADED TIP DIPOLE MICROWAVE ANTENNA”. The size andshape of the sheath 338 and the coolant chamber 337 extendingtherethrough may be varied from the configuration depicted in FIG. 3.

Electrosurgical system 1000 in accordance with an embodiment of thepresent disclosure includes a power generating source 328, a coolantsupply system 313 adapted to provide coolant fluid “F” via a connectionhub 322 to the antenna assembly 312, and a sensor unit 346 capable ofdetecting a gas bubble in the coolant supply system 313 and electricallycoupled via transmission lines 301 and 302 to the power generatingsource 328. Electrosurgical system 1000 may further include aflow-diverter apparatus 350 operably associated with the sensor unit 346and disposed in fluid communication between the sensor unit 346 and theconnection hub 322. In some embodiments, when the sensor unit 346detects an air or other gas bubble in the coolant supply system 313, thesensor unit 346 transmits an electrical signal via transmission line 302to the power generating source 28 and the flow-diverter apparatus 350.Sensor unit 346 and the power generating source 328 are similar to thesensor unit 46 and the power generating source 28, respectively, shownin FIG. 1 and further description thereof is omitted in the interests ofbrevity.

Coolant supply system 313 generally includes a coolant source 336, afirst coolant path 319 leading from the coolant source 336 to theconnection hub 322, and a second coolant path 320 leading from theconnection hub 322 to the coolant source 336. In some embodiments, thefirst coolant path 319 includes a first fluid movement device 344configured to move coolant fluid “F” through the first coolant path 319,and the second coolant path 320 includes a second fluid movement device334 configured to move coolant fluid “F” through the second coolant path320. Coolant source 336 stores coolant fluid “F”, and may maintaincoolant fluid “F” at a predetermined temperature. For example, thecoolant source 336 may include a cooling unit (not shown) that cools thereturning coolant fluid “F” from the antenna assembly 312.

Connection hub 322 may have a variety of suitable shapes, e.g.,cylindrical, rectangular, etc. In some embodiments, the connection hub322 includes a cable connector 379, an outlet fluid port 330 and aninlet fluid port 332. Connection hub 322 may include a three-branch luertype connector 372 having a middle branch 374 used to house the cableconnector 379 and two outer branches 376 and 378 to house the outlet andinlet fluid ports 330 and 332, respectively. Connection hub 322 may beformed of any of a variety of materials, e.g., any suitablenon-conductive conformal material. Examples of non-conductive conformalmaterials that may be suitable for forming the connection hub 322include polyesters, polyimides, polyamides, polyamide-imides,polyetherimides, polyacrylates, polyethylene terephthalate,polyethylene, polypropylene, polyvinylidene chloride, polysiloxanes,combinations thereof and the like.

Connection hub 322 may be adapted to be connected in fluid communicationwith the sheath 338. In some embodiments, the sheath 338 is coupled tothe connection hub 322 and the tip 123, thereby defining a chamber 337around the feedline 110, the proximal radiating portion 140 and thedistal radiating portion 105.

In some embodiments, the first coolant path 319 includes a coolantsupply line 386 leading from the coolant source 336 to the inlet fluidport 332. First fluid movement device 344 may be disposed in fluidcommunication between the inlet fluid port 332 and the coolant source336. In some embodiments, the second coolant path 320 includes a coolantreturn line 388 leading from the outlet fluid port 330 to the coolantsource 336. Second fluid movement device 334 may be disposed in fluidcommunication between the outlet fluid port 330 and the coolant source336. The positions of the first fluid movement device 344 and the secondfluid movement device 334, e.g., in relation to the coolant source 336,may be varied from the configuration depicted in FIG. 3.

In some embodiments, a controller 351 associated with the flow-diverterapparatus 350 may actuate a fluid flow diverter 352 to divert coolantfluid “F” flow to a third coolant fluid path 321. Fluid flow diverter352 may be any suitable device for selectively diverting the coolantfluid “F” flow. Third coolant fluid path 321 may lead from theflow-diverter apparatus 350 to a container 390. Controller 351 mayinclude any type of computing device, computational circuit, or any typeof processor or processing circuit capable of executing a series ofinstructions that are stored in a memory (not shown) of the controller351.

In some embodiments, the flow-diverter apparatus 350 includes a valve(not shown) that includes a valve body and an electromechanical actuatoroperatively coupled to the valve body. Controller 351 may control fluidflow diverter 352 by activating the actuator, e.g., according to apredetermined valve control sequence. In some embodiments, a valvecontrol sequence may involve moving the valve from a first position, inwhich coolant fluid “F” flows towards the connection hub 322, to asecond position, in which the coolant fluid “F” having an air or othergas bubble entrained therein flows into the container 390, and returningto the first position, e.g., after a predetermined time interval,thereby re-establishing coolant fluid “F” flow towards the connectionhub 322.

Hereinafter, methods of optical detection of interrupted fluid flow toan electrosurgical device, in accordance with the present disclosure,are described with reference to FIGS. 4 through 6. It is to beunderstood that the steps of the methods provided herein may beperformed in combination and in a different order than presented hereinwithout departing from the scope of the disclosure.

FIG. 4 is a flowchart illustrating a method of detecting a bubble in afluid flow according to an embodiment of the present disclosure. In step410, an optical sensor unit (e.g., 46 shown in FIG. 1) is provided thatincludes a light-emitting element (e.g., 43 shown in FIG. 1) and alight-receiving element (e.g., 40 shown in FIG. 1). The optical sensorunit is operably associated with a fluid path (e.g., 19 shown in FIG.1). In some embodiments, the light emitting element and light-receivingelement are disposed such that light directed from the light-emittingelement passes through the fluid path to the light-receiving elementduring the fluid flow in the fluid path.

In step 420, a first reference value is determined based on an air flowin the fluid path passing through the optical sensor, and a secondreference value is determined based on a fluid flow in the fluid pathpassing through the optical sensor unit. As illustrated in FIG. 5, step420 may further include steps 421 and 422. In step 421, light from thelight-emitting element is directed through the air flow in the fluidpath passing through the optical sensor unit and a characteristic oflight collected at the light-receiving element is sensed to determinethe first reference value. In step 422, light from the light-emittingelement is directed through the fluid flow in the fluid path passingthrough the optical sensor unit and a characteristic of light collectedat the light-receiving element is sensed to determine the secondreference value. In some embodiments, the sensed characteristic of lightis an intensity of light collected at the light-receiving element. Inother embodiments, the sensed characteristic of light is an absence oflight incident on the light-receiving element.

In step 430, the optical sensor unit is used to monitor the fluid flowin the fluid path to detect an air bubble in the fluid flow using atleast one of the first reference value or the second reference value. Insensor unit embodiments using signal intensity to detect an air bubble,the change in intensity of light collected at the light-receivingelement is interpreted as indicator of the presence of an air bubble.

In step 440, when an air bubble in the fluid flow is detected by theoptical sensor unit, an electrical signal is transmitted from theoptical sensor unit. In some embodiments, when the sensor unit detectsan air (or other gas) bubble in the coolant supply system, the sensorunit transmits an electrical signal to a power generating source (e.g.,28 shown in FIG. 1).

FIG. 6 is a flowchart illustrating a method of detecting a bubble in afluid flow according to an embodiment of the present disclosure. In step610, a fluid source (e.g., 336 shown in FIG. 3) for supplying a fluid(e.g., “F” shown in FIG. 3) is provided. The fluid source may includeany suitable source, e.g., a container of coolant ordielectric-buffering fluid.

In step 620, an optical sensor unit (e.g., 346 shown in FIG. 3) isprovided that includes a light-emitting element (e.g., 43 shown in FIG.3) and a light-receiving element (e.g., 40 shown in FIG. 3) The opticalsensor unit is operably associated with a fluid path (e.g., 319 shown inFIG. 3), the fluid path leading from the fluid source to anelectrosurgical device (e.g., 312 shown in FIG. 3) operably associatedwith an electrosurgical generator (e.g., 328 shown in FIG. 3).

In step 630, a first calibration step is performed by directing lightfrom the light-emitting element through an air flow in the fluid pathpassing through the optical sensor unit and a characteristic of lightcollected at the light-receiving element is sensed to determine a firstreference value.

In step 640, a second calibration step is performed by directing lightfrom the light-emitting element through a fluid flow in the fluid pathpassing through the optical sensor unit and a characteristic of lightcollected at the light-receiving element is sensed to determine a secondreference value.

In step 650, the optical sensor unit is operated to direct light fromthe light-emitting element through the fluid flow in the fluid pathpassing through the optical sensor unit and a characteristic of lightcollected at the light-receiving element is sensed to determine a thirdreference value.

In step 660, an electrosurgical generator, which may be used to activatethe electrosurgical device, is controlled based on a comparison resultof a comparison of the third reference value to the first referencevalue and the second reference value. In some embodiments, the opticalsensor unit is electrically coupled to the electrosurgical generator.Based on the comparison result, the optical sensor unit may output anelectrical signal to the electrosurgical generator and, in responsethereto, the power output of the electrosurgical generator may bereduced, e.g., for a predetermined time interval or until a manual resetswitch is actuated. In some embodiments, the optical sensor unit outputsan electrical signal when the third reference value is determined to besubstantially equal to the first reference value.

In some embodiments, the fluid flow may be diverted by a flow-diverterapparatus (e.g., 350 shown in FIG. 3) to a different fluid path (e.g.,321 shown in FIG. 3) for a predetermined period of time based on thecomparison result. The predetermined period of time may be a period oftime to allow for the air bubble to pass out of the fluid path (e.g.,319 shown in FIG. 3) that leads to the electrosurgical device and,instead, into a different fluid path (e.g., 321 shown in FIG. 3), e.g.,leading to a container (e.g., 390 shown in FIG. 3). In some embodiments,the electrosurgical system (e.g., 1000 shown in FIG. 3) controlselectrical characteristics of the electrosurgical generator todeactivate the electrosurgical device (e.g., 312 shown in FIG. 3) duringthe predetermined time period.

Although embodiments have been described in detail with reference to theaccompanying drawings for the purpose of illustration and description,it is to be understood that the inventive processes and apparatus arenot to be construed as limited thereby. It will be apparent to those ofordinary skill in the art that various modifications to the foregoingembodiments may be made without departing from the scope of thedisclosure.

1. An electrosurgical system, comprising: an electrosurgical deviceadapted to direct energy to tissue; an electrosurgical generator foractivating the electrosurgical device; a fluid path leading to theelectrosurgical device; an optical sensor unit operably associated withthe fluid path, the optical sensor unit including: a light-emittingelement to generate light output; and a light-receiving element tocollect light outputted from the light-emitting element, wherein thelight-emitting element and the light-receiving element are disposed suchthat light output from the light-emitting element passes through thefluid path to the light-receiving element; wherein the optical sensorunit is capable of detecting an air bubble in the fluid path passingthrough the optical sensor unit using a sensed characteristic of lightcollected at the light-receiving element; a flow-diverter apparatusoperably associated with the optical sensor unit and disposed in fluidcommunication with the fluid path between the optical sensor unit andthe electrosurgical device; and a container for collecting fluiddiverted by the flow-diverter apparatus.
 2. The electrosurgical systemof claim 1, wherein the sensed characteristic of light is an intensityof light collected at the light-receiving element.
 3. Theelectrosurgical system of claim 1, wherein the sensed characteristic oflight is an absence of light incident on the light-receiving element. 4.The electrosurgical system of claim 1, wherein electrical output of theelectrosurgical generator is controlled based on an electrical signalreceived from the optical sensor unit, wherein the electrical signal isgenerated by the optical sensor unit in response to detection of an airbubble in the fluid path.
 5. The electrosurgical system of claim 1,wherein the optical sensor unit outputs an electrical signal to theelectrosurgical generator and the flow-diverter apparatus in response todetection of an air bubble in the fluid path.
 6. The electrosurgicalsystem of claim 5, wherein a direction of fluid flow is controlled bythe flow-diverter apparatus based on the electrical signal, andelectrical power output of the electrosurgical generator is controlledbased on the electrical signal.
 7. The electrosurgical system of claim6, wherein the flow-diverter apparatus further includes: a controllerelectrically coupled to the optical sensor unit; and a fluid flowdiverter operably associated with the controller to divert fluid flow tothe container.
 8. The electrosurgical system of claim 7, wherein, inresponse to the electrical signal from the optical sensor unit, thecontroller actuates the fluid flow diverter to divert fluid flow to thecontainer.
 9. The electrosurgical system of claim 8, wherein, after apredetermined time period, the controller actuates the fluid flowdiverter to re-divert fluid flow to the fluid path.
 10. Theelectrosurgical system of claim 9, wherein the controller iselectrically coupled to the electrosurgical generator and adapted tooutput electrical signals indicative of the predetermined time period,wherein the electrosurgical generator is controlled based on theelectrical signals indicative of the predetermined time period todeactivate the electrosurgical device during the predetermined timeperiod.